Once the exclusive province of elite athletes, interval
training is becoming almost de rigueur for health researchers around the world.
If intermittent short sprints were a drug, pharmaceutical companies would be
spending millions to acquire patent rights. But intervals are free to anyone
willing to invest a few minutes of sweat equity every week.

Sixteen sedentary or recreationally active young men (and 9
controls) were tested for glucose tolerance and insulin sensitivity before and
after two weeks of supervised interval training totaling just 15 minutes of high
intensity exercise. The training included 6 every-other-day sessions of 4 to 6
30-second all-out cycle sprints, with 4 minutes recovery between sprints.
Including rest periods, the time commitment over two weeks was approximantly135
minutes, a little over 2 hours—far less than traditional endurance regimens.

Among other results, blood glucose level was significantly
reduced (12%) after two weeks of interval training. The blood sugar response
after drinking 75 grams of glucose (simple sugar) was substantially less after
training than before; rather than spike after 60 minutes, as it did before
training, blood sugar level remained essentially unchanged. Likewise, insulin
response to oral glucose was also significantly reduced (37%) after two weeks of
training, indicating that insulin sensitivity was substantially improved. In
short, insulin did a better job clearing glucose from the bloodstream after
interval training.

Another test showed that insulin sensitivity was improved
by 23% after two weeks of training.

Importantly, the improvement in glucose clearance from the
bloodstream lasted for up to 10 days after the final exercise session.

The Muscle Factor

In the Discussion portion of their report, the
researchers highlight two features of short duration high-intensity interval
training (HIT), which set it apart from walking or moderate intensity aerobic
training. Both distinguishing features involve muscle.

HIT works your muscles much more than steady-state moderate
aerobic exercise. (For an explanation of how muscle fibers are activated, see “Forget
Heavy, Think Effort”
http://www.cbass.com/Carpinelli.htm )

“HIT has as least two novel features,” the researchers
write. “[First], it involves the activation of a large muscle mass; secondly,
this is associated with a very high glycogen breakdown-turnover.” (Glycogen is a
form of carbohydrate (glucose) stored in muscles (and the liver); it is released
as needed for energy.)

Why is that important?

“The combination of these two factors means that a greater
proportion of muscle fibers will need to replenish their carbohydrate stores.”

In other words, interval training causes the glucose in
your blood to be converted to glycogen in your muscles. Shazam!
Lower blood sugar.

Makes sense, doesn’t it.

Bottom line: Short, hard intervals do a better job
than steady-state aerobic training keeping your blood sugar on an even keel and
lowering your risk of developing adult onset diabetes. And they do it in a
fraction of the time. What’s more, intervals are more challenging and fun. For
most people, steady state aerobic exercise is boring.

If you are out of shape or have health problems, you should
consult your doctor before embarking on an interval training program. In any
event, start slowly and increase intensity gradually as your
condition improves.